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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The Key Studies of Kishi et al. (1990) and Southworth and Keller (1986) report measured Koc values in widely varied soils, which range from 876 - 3,300 (log Koc 2.94 - 3.52).  Other supporting studies of Saeger et al. indicate log Koc values ranging from 2.16 - 2.38 in various aquatic sediment samples. A QSAR prediction of log Koc = 3.15, using a recently developed QSAR for neutral organics, is also reported by Schüürmann et al. (2006).  The average value of eight well-documented log Koc values reported in the Key Studies (ave. log Koc = 3.19) will be used as basis for the Chemical Safety Assessment.  

Key value for chemical safety assessment

Koc at 20 °C:
1 546

Additional information

The Key Studies provide the best available and relevant measured values of log Koc for this substances. Several databases and studies refer to an experimentally determined log Koc value of 3.27 for biphenyl, which turns out to be an average of estimated log Koc values determined for various samples of colloidal organic matter. This 1984 study by Landrum et al. (Environmental Science and Technology 18:187 -192) has no similarity to current standardized test guidelines. The experimental database of U.S. EPA KocWIN refers to Schüürmann et al. (2006), Schüürmann et al. refer to a publication of Sabljic et al. (1995), which cites the average log Koc value of Landrum et al. (1984).

Further, several reliable QSAR estimates are available. Using KocWIN v2.00, which is an approved tool for estimating adsorption coefficients for organic substances, the log Koc was predicted to be 3.71 based on first order molecular connectivity index, and 3.47 based on log Kow. A newly developed QSAR for neutral organics however yields a most likely more reliable value of 3.15 (Schüürmann et al., 2006).

Three other sources yielded relevant, but non-reliable information. The environmental fate studies of Saeger et al. (1988a,b,c) – described under the endpoints on biodegradation – yielded log Koc values of 2.25, 2.16 and 2.27-2.38, respectively. These values could not be considered reliable because of the interference of other loss processes (e.g., volatilization, degradation, adsorption to testing equipment, etc.). However, the fact that they are lower than the experimentally determined value as well as the available estimates is completely in line with the expectations based on the rationale for these studies and therefore these values can be used in support of the other available information.

[LogKoc: 3.19]